1. Field of the Invention
The present invention relates to paired electrical conductors in cables used for transmitting both digital and analog signals and, more particularly, to twisted pair cables.
2. Brief Description of Related Developments
It has been the practice for many years that signals being communicated electrically in communication networks be transmitted over twisted pairs of signal conductors. This has been true for telephony signals and other types of signals, both analog and digital, including signals passed in computer networks and sometimes within the computer assemblies.
The reasons that twisted pairs of signal conductors are used include controlling crosstalk between signal paths provided by various pairs which pass in close proximity to one another, such as being cabled together. In multi-pair cabling, two primary approaches have been used to control crosstalk. One is to have each pair in the cable twisted at a different twist rate (that is, the numbers of twists or turns per increment of length—a pair may be described as twisted at five turns per foot, for example). Another is to wrap each pair in a foil shield. Either approach imposes difficulties in manufacture, which conventional practice has come to accept.
Differing twist rates in twisted pairs which are cabled together, while effective in some control of crosstalk, presents other difficulties as signal rates through such pairs are increased. In particular, twisting pairs at different twist rates results in pairs which have differing physical lengths within a given length of cable thus resulting in differing signal propagation delay characteristics. For demanding applications such as 1-10 Gbps Ethernet, such differing physical lengths are a significant impediment as it is desirable to have as close as possible to simultaneous delivery of the transmissions on all pairs in a cable. Thus the capabilities of conventional twisted pair cables become marginal or unacceptable.
Thus, there exists a need to provide a cable having twisted pairs therein with different twist rates changing continuously over the length of the cable and an apparatus to make such a cable.